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Multimedia Messaging Service (MMS) is a standard way to send messages that include multimedia content to and from mobile phones. It extends the core SMS (Short Message Service) capability that allowed exchange of text messages only up to 160 characters in length.
The most popular use is to send photographs from camera-equipped handsets. It is also used on a commercial basis by media companies as a method of delivering news and entertainment content and by retail brands as a tool for delivering scannable coupon codes, product images, videos and other information. Unlike text only SMS, commercial MMS can deliver a variety of media including up to forty seconds of video, one image, multiple images via slideshow or audio plus unlimited characters.
Multimedia messaging services were first developed as a captive technology that would enable service providers to "collect a fee every time anyone snaps a photo."
Early MMS deployments were plagued by technical issues and frequent consumer disappointments, but in recent years MMS deployment by major technology companies have solved many of the early challenges through handset detection, content optimization, increased throughput, etc.
China was one of the early markets to make MMS a major commercial success partly as the penetration rate of personal computers was modest but MMS-capable cameraphones spread rapidly. The chairman and CEO of China Mobile said at the GSM Association Mobile Asia Congress in 2009 that MMS in China is now a mature service on par with SMS text messaging.
Europe's most advanced MMS market has been Norway and in 2008 the Norwegian MMS usage level had passed 84% of all mobile phone subscribers. Norwegian mobile subscribers average one MMS sent per week.
Between 2010 and 2013, MMS traffic in the U.S. increased by 70% from 57 Billion to 96 Billion messages sent.  One of the main reason behind increase in MMS traffic is decrease of usage of proprietary Mobile Operating Systems, as they had different implementations for enconding and MMS message handling. As most of the smartphones are running Android, MMS encoding and implementation gets generalized hence usage of MMS has been increased substantially.
MMS messages are delivered in a completely different way from SMS. The first step is for the sending device to encode the multimedia content in a fashion similar to sending a MIME e-mail (MIME content formats are defined in the MMS Message Encapsulation specification). The message is then forwarded to the carrier's MMS store and forward server, known as the MMSC (Multimedia Messaging Service Centre). If the receiver is on another carrier, then the MMSC [acts as a relay, and] forwards the message to the MMSC of the recipient's carrier using the Internet.
Once the recipient's MMSC has received a message, it first determines whether the receiver's handset is "MMS capable", that it supports the standards for receiving MMS. If so, the content is extracted and sent to a temporary storage server with an HTTP front-end. An SMS "control message" containing the URL of the content is then sent to the recipient's handset to trigger the receiver's WAP browser to open and receive the content from the embedded URL. Several other messages are exchanged to indicate status of the delivery attempt. Before delivering content, some MMSCs also include a conversion service that will attempt to modify the multimedia content into a format suitable for the receiver. This is known as "content adaptation".
If the receiver's handset is not MMS capable, the message is usually delivered to a web based service from where the content can be viewed from a normal internet browser. The URL for the content is usually sent to the receiver's phone in a normal text message. This behaviour is usually known as the "legacy experience" since content can still be received by a phone number, even if the phone itself does not support MMS.
The method for determining whether a handset is MMS capable is not specified by the standards. A database is usually maintained by the operator, and in it each mobile phone number is marked as being associated with a legacy handset or not. This method is unreliable, however, because customers can change their handset at will, and many of these databases are not updated dynamically.
MMS does not utilize one's own operator maintained data plan to distribute multimedia content. Operator maintained data plans are only used when message included links (if any) are explicitly clicked.
E-mail and web-based gateways to the MMS (and SMS) system are common. On the reception side, the content servers can typically receive service requests both from WAP and normal HTTP browsers, so delivery via the web is simple. For sending from external sources to handsets, most carriers allow MIME encoded message to be sent to the receiver's phone number with a special domain. An example of this would be PTN@messaging.carrier.com, where PTN is the public telephone number. Typically the special domain name is carrier specific.
There are some interesting challenges with MMS that do not exist with SMS:
Although the standard does not specify a maximum size for a message, 300 kB is the current recommended size used by networks due to some limitations on the WAP gateway side.